Television synchronizing system



Aug-25,1941!- M. CAWEIN 2,294,072

TELEVISION SYNCHRONIZING SYSTEM Filed Dec. 17, 1938 FIG.1

RE MOD. 501mm VIDEO VIDEO VIDEO PICTURE *VIDEOLE LE *DEI "AMR REPRODUCER 1- Z- 3- 5- 6 ,7 ,8' 9

OSC. LF.

SERRATED s? 10 w AE L 11 38 SUPPRESSOR E -2 2- SUIEiFSSOR H62 INVENTOR. M40150 CA'WEl/V A TTORNEY.

Patented Aug. 25, 1942 UNITED STATES PATENT OFFICE TELEVISION SYNCHRONIZING SYSTEM Madison Cawein, Manhasset, N. Y.

Application December 17, 1938, Serial No. 246,260

3 Claims.

The present invention relates to television synchronizing systems and in particular to a method of, and meansior, synchronizing television picture field periodicity by amplitude selection of the serrated region of a standard synchronizing wave.

One object of the present invention is to improve field synchronizing in television reception by adding amplitude selection to the standard field synchronizing signal. 4

Another object is to provide this amplitude selection in the receiver and thereby provide the advantages of such a system while maintaining the advantages and economy of transmission of the standard synchronizing signal.

Still another object is to provide a method of, and means for, maintaining field synchronism in a television receiver even in the absence of received signals as for instance in the presence of strong fading.

These and further objects of this invention will be evident from the following description and in particular from the detailed description of the various figures of the drawing. I

In an interlaced television system it has been usual to synchronize the scanning mechanisms of the television receiver by means of synchronizing signals which are transmitted as modulations of a carrier signal, which is also modulated with video signals conveying the picture detail.

Further, these synchronizing signal modulations usually consist of amplitude modulations which line outside the amplitude range of the video modulations to facilitate the separation of synchronizing signals from video signals by amplitude separating means which are provided at the receiver.

After separation from the video signals the synchronizing signals contain information which maly be utilized to synchronize the line scanning mechanism of the receiver and information which may be utilized to synchronize the field scanning mechanism of the receiver. It is usual to separate the line synchronizing information from the field synchronizing information to prevent undesirable efiects of one upon the other. The two kinds of synchronizing information are frequently conveyed by means of what is well known in the art formation. Unfortunately, there are difficulties in the transmission of a signal having amplitude diiierences and these have been thought to outweigh the advantages, so that a type of serrated signal without this amplitude difference has come into general use.

The present invention provides means whereby a desired amplitude difference between line and frame synchronizing signals may be obtained at the receiver in order to secure a more acurate and stable interlace and an improved synchronization of the field scanning means, without any change in the form of the standard transmitted signal. This improved operation is obtained by multiplying or by mixing the serrated region of the field framing and interlace synchronizing signals, with pulses of field frequency voltage. One method of accomplishing this multiplication, which results in the desired amplitude difference in the serrated region, is to mix the synchronizing signals with power line or other suitable field frequency pulses in a suitable mixer tube. In order to produce'a maximum of accuracy and stability in this system, further means are provided for varying the phase of the field frequency pulses.

In general, this phasing means is utilized to take into account the phase of the transmitted signals with respect to the power line, the transmission path of the modulated signals and the phase characteristics'of the power line between transmitter and receiver as well as the receiver circuits between the power line and the point at which the pulses are taken off; A further function and advantage may be gained with this system in that a television receiver field may be kept in synchronism with the transmitter even in the absence of received signals. When this is not done, loss of synchronizing signal causes the picture field at the receiver to change size and texture, which is displeasing to an observer.

It is a standard practice to make the periodicity or frequency of repetition of the serrated field synchronizing region of a standardized television synchronizing wave identical with the power-line frequency, and in fact, to synchronize the former with the latter, at sixty cycles per second in the United States. This synchronization has been effected in order to prevent undesirable hum distortions and weavings of interlace which can occur due to insufiicient filtering of the receiver power supply. There exists, therefore, in the receiver power supply circuit a potential wave of periodic amplitude, and of correct frequency for mixing with the synchronizing wave if the power supply voltage is supplied in the proper nizing wave over the serrated region to a greater amplitude than that existing in other regions of .the synchronizing wave.

This invention will be better understood from the following detailed description when taken with reference to the drawing in which:

Fig. 1a is a section of a standard synchronizing signal wave as at present practiced in the United States, as it appears in the serrated region of every field.

Fig. lb is the peak amplitude of the power line potential wave and certain harmonic components, adjusted in proper phase to coincide in time with the serrated region of the synchronizing wave.

2,294,072 Y phase, to increase the amplitude of the synchro- Y quency, the wave form of which is usually rich in harmonics due to transformer loading and may be as shown by curve I. The resistor 3| may be included in the full-wave-rectifled-current path of the power supply, in which case there will exist at its terminal D the well known fullwave-rectification potential of the A. C. power Fig..1c is a mixture or multiplication of the wave forms of Figs. 1a and 1b, as produced in accordance with this invention, at the output of the mixer amplifier of Fig. 2.

Fig. 2 is a combined block and schematic representation of a television receiver in accordance with this invention.

More particularly, referring now to Fig. 2, I is the antenna of a television receiver which supplies received signal to an r-,f amplifier and tuning or selector unit 2. If the receiver is of the superheterodyne type it may include an oscillator 3 and a modulator 4 for producing and applying an intermediate frequency signal to the intermediate frequency amplifiers 5, 6, and ID of the receiver, which, are, however, not necessary to the objects of this invention as will be understood by those familiar with the art.

The receiver may include a sound channel II and a loud speaker l2. The receiver will usually include a detector 1 which demodulates the signal wave to supply picture signals to a video channel 8 and/or to the picture reproducing means 9, which may include a cathode ray tube, and which will include line scanning and synchronizing mechanisms L, and field or frame scanning and synchronizing means F.

For purposes of clarity a circuit has been included in Fig. 2, and designated generally by M, as shown and described in my copending application entitled Television synchronizing and control system filed on October 5, 1938, and bearing Serial No. 233,372 as a means of separating the synchronizing modulations from the video modulations in the received signal in order to produce at G a standard synchronizing wave free from video signals. A serrated section of this wave has, beenshown in Fig. la. The circuit M may in certain applications be a part of the detector 1, or of the video channel 8, and will usually include a fast A. V. C. filter 38 and an A. V. C. connection 31.

The synchronizing wave at G is applied to the control grid I5 of a mixing amplifier tube l6, by means of blocking condenser I3 and across grid leak l4. Tube It also includes a cathode 36, a plate 39, suppressor grid i1 and screen grid l8, although other types of mixer tubes or means may be used.

The receiver will include also a power supply consisting of a plate transformer 24 and a heater transformer 25 which may be combined in one unit, and which may be connected to the power line 26 by the switch 21. The transformer 24 supplies D. C. potential to the various units of the receiver by way of the rectifier 28, the power filter 30, and the connector 33. Transformer 25 supplies A. C. potential to the receiver by way of connectors 34 and 35. The point e on the connector 34 has a cyclic potential at power-line freline which usually contains a small component of the power-line frequency, as well as many of its harmonics, due to circuit unbalance, as shown, in curve J or which may be made to contain such by deliberate insertion of the resistor 29 in series with one plate terminal of the rectifier. E is a terminal connector on a plate of-the rectifier, atwhich there exists a distorted potential wave of power line and harmonic frequencies as shown in curve K. The suppressor ll of the mixing amplifier I6 is biased beyond cut-off via resistor 20 from a point on resistor 32 placed in the return path of the power supply current and bypassed by condenser 32' so that the tube I3 is normally inoperable. By connecting terminal A to terminal C, and by adjusting the small condenser |9 and/or resistor 20 to obtain a desired amplitude and phase of power-line voltage plus its harmonics, the suppressor I! may be driven positive for any desired fraction and at any desired phase of the power-line cycle, as shown in Fig. lb to interrupt suppressor cut-off and thus allow plate current to fiow in the plate circuit of the pentode 16. As set forth above, the field frequency voltage may be obtained from points D or E as well as C by connecting point A to any of these points.

The flow of plate current in the load resistor 23 of the pentode IE will be controlled by the combination of signals at the control grid l5 and at the suppressor grid II. If the phase and duration of the suppressor signal above suppressor cut-off is adjusted properly to coincide substantially with that of the serrated region of the synchronizing signal on the control grid, the output at terminal H of the pentode l6 can be made to consist of only a portion of the serrated region of the synchronizing wave of Fig. 1a, modified by the form of the rise and fall oi. suppressor potential above suppressor cut-off level as shown in Fig. 1c, and by virtue of the synchronism which exists between power-line frequency and field frequency as has been described.

The wave of Fig. 10 will be repeated in each power-line cycle and can be adjusted by the phasing means described to repeat identically in each cycle. This wave may be supplied via terminal H to synchronize the field scanning mechanism of a television receiver, as for example to synchronize the grid of a field relaxation oscillator, which constitutes part of a field scanning means for a cathode ray tube.

A similar operation may be obtained by applying the field frequency signal to screen grid l8 by connecting point B to one of points C, D or E or such voltages may be applied to both screen I 8 and suppressor I1. Phasin of voltage on screen [8 may be obtained'by adjustment of condenser 2| and/or resistor 22.

It will be obvious to those skilled in the art that signals of the proper field periodicity and of proper wave form can be supplied from many points on a television receiver other than the points C, D and E shown in Fig. 2, and may be applied to the suppressor grid ll-of the mixing amplifier IS without departure from the spirit of this invention. In fact, a field bump" or complex alternating potential wave at field frequency and containing harmonic components of that frequency, usually exists across some connection in the A. V. C. system, due to fast time constant, or insufiicient filtering of the low frequency components of the video wave, as for instance at connection 31 to filter 36 in the A. V. C. circuit of the means shown at M in Fig. 2.

It will be further obvious to those skilled in the art that the mixing action which has been described, and which emphasizes the amplitude of one portion of the synchronizing wave, may be augmented by simultaneously or alternatively supplying one of the potential waves I, J or K to other grids of the amplifier l6 as for instance to the screen grid l8 via adjustable condenser 2| and screen resistor 22.

In the absence of a television signal wave the field scanning means can be held in synchronism with the power-line frequency by virtue of the control action of suppressor and/or screen grid of amplifier l6 which action will repeat a fieldbump" signal of power-line periodicity into the plate circuit of the pentode IS. The amplitude of this signal may be adjusted by proper choice of circuit constants so that it is suflicient to synchronize the field scanning mechanism.

The polarity of the synchronizing signals has been shown as positive at the terminal H, by way of illustration, since this is a polarity of frame synchronizing signal that is often required. It will be apparent to those skilled in the art that the reverse polarity of synchronizing signal may be obtained by simple means, such as the use of an extra stage of amplification, and that other types of mixing may beemployed, such as an array of amplifiers in parallel or a network of electrical impedances having a common branch, without departing from the spirit of this invention.

While I have shown and described one form of my invention other forms and modifications are possible within the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. In a television receiver, the combination of,

a synchronizable field sweep signal generator, means for receiving composite television picture and synchronizing signals, means for deriving field synchronizing signals from said composite signals, means for deriving discrete field frequency signals, means for distorting said field frequency signals, means for deriving a predetermined component of said distorted signals, means for mixing said predetermined component with said field synchronizing signals, and means for synchronizing said generator in accordance with said mixed signals.

2. In a television receiver, the combination of, synchronizable field sweep signal generating means, means for deriving field synchronizing signals from composite received signals, a thermionic vacuum tube including at least two input electrodes and one output electrode, means for deriving a signal from a local alternating current power source, means for applying said signal from said local source to one of said input electrodes, means for applying said field synchronizing signals to another of said input electrodes and means for applying at least a portion of signals from said output electrode to said field sweep generating means. i

3. In a television receiver, the combination of, field sweep generating means, means for deriving field synchronizing signals from composite received signals, a thermionic vacuum tube in-- cluding at least two input electrodes and one output electrode, means for applying at least a portion of a local power alternating current voltage to one of said input electrodes, means for varying the phase of said voltage applied'to said electrode, means for applying said synchronizing signals to another of said input electrodes, and means for applying at least a portion of voltages on said output electrode to said field sweep generating means whereby said local power voltage is combined with said field synchronizing signals to provide a composite signal for MADISON CAWEIN. 

